This gets more complicated as I dig further. I wasn't aware that there's two sensors and the videos make no mention of it at all when showing how to replace one with a contactless unit. It's frustrating when detailed knowledge is assumed and just glossed over.
More frustrating is that Volvo Diagnostic no longer repair these throttle bodies.

Another thought is, I haven't got the throttle body off at the moment but, if the sensor at the back is one of those smaller ones advertised at less than a tenner on the internet, I'd be as well trying replacing that one first?

again im not 100% sure but I was under the impression both sensors were the same type

how you would identify which one was dodgy I have no idea

and the replacement procedure for the £80 sacer unit (1 x kit bought as a single unit to completely repair) is the same either way anyway regardless of which one died ?

unless anyone comes along and tells us differently

Looks like I'm going down the DIY replacement route.
Wish me luck!

I have no idea how it works[I'm not that clever]but on mine there are two "end caps" -the black square thing shown in the picture-held on by four screws-of these you only replace the "inner" one and there's a wire from that that goes to the "outer" one which you have to modify by cutting off one of the contacts.The instructions which came with the Sacer I bought shows this.You shouldn't have to remove the "outer" cap but if for some reason you do be very very careful as there are two extremely thin copper wires at the top attaching something on the cap to something inside the throttle body and they're easily broken requiring some very awkward and delicate soldering to fix.

Installing the Sacer kit is really easy - check out my post on it.

agreed it wasn't difficult really, as already stated logistically in terms of programming and the cost of replacement TB, it could be the best choice

the debate on it now is, if Lucas at Volvo Diagnostic said they were getting hit and miss (and they were doing proper bench testing on them) then that's probably worth bearing in mind as a fact

that may have been the reason my repair didn't work. or maybe my fault was something unrelated. it's always possible I did it wrong, but I don't think so, as you say it is fairly straight forward

all in all though, cost wise, it still makes sense to give it a go before trying more expensive solutions

I think you'll find[although I'm by no means an expert so could be wrong]that those small sensors at less than a tenner fit the cars with an actual throttle cable and not, despite what e-bay might say,the "drive by wire"cars such as yours.Now to throw a spanner in the works/cause a bit more confusion as a "drive by wire" car you will have a throttle position sensor at the pedal end too! Whether if this goes wrong it exhibits the same symptoms as the throttle body ones or if it has a different fault code I don't know but it could be worth checking the connection and perhaps cleaning the connectors with some contact cleaner?

There is also an alternative to the Sacer units and that is using a lada tps sensor. First I've heard about it, but worth a try.

Secondly, there are two types of ETMs, one for regular 2.4i and one for 2.4i bifuel. The bifuel variants ran up to 2007 and the software for them was the old one where you couldn't use VIDA to monitor the internal TPS'es. And the algorithms for determining faults weren't as good. As such even a 2007 bifuel model could fail at the last moment with no early warning.

I also believe some later 2.4i engines had the legendary Bosch throttle unit, but it operates in a very different manner. Unlike the ETM, the bosch throttle unit requires a separate PWM driver(integrated in the ECM) as it has no electronics inside, unlike the ETM which is a standalone unit and how it works is via CAN.

The engine sends a Requested throttle position and the ETM tries to comply with an Effective(actual) throttle angle using internal PWM driver for the throttle plate motor.

Issue diagnosed by an independent Volvo specialist who advised a new throttle body or send for repair.
Not being able to find a suitable repairer, I bought a contactless replacement TPS and went about fitting it myself, not too difficult although digging out the silicone around the contacts was a bind. Interestingly, the instructions tell you to cut off the rotating shaft and then unscrew the base nut - not a good idea as you're left with nothing to grip when trying to unscrew an exceedingly tight nut! The contact prongs on the new TPS were pretty short but I'd already decided to hand over the soldering of the new connections to my local auto electrical specialist - he only wanted a fiver but I couldn't give him less than a tenner for a job like that!
Now fitted and the engine is running much smoother and no coughing on acceleration. Job well done.